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参数资料
| 型号： | LT1777CS |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| 中文描述： | 1 A SWITCHING REGULATOR, 115 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | 0.150 INCH, PLASTIC, SO-16 |
| 文件页数： | 15/24页 |
| 文件大小： | 270K |
| 代理商： | LT1777CS |
15
LT1777
However, remember that oscillator slowdown to achieve
short-circuit protection (discussed above) is dependent
on FB pin behavior, and this in turn, is sensitive to FB node
external impedance. The graph in Figure 7 shows the
typical relationship between FB pin voltage, driving im-
pedance and oscillator frequency. This shows that as
feedback network impedance increases beyond 10k, com-
plete oscillator slowdown is not achieved, and short-
circuit protection may be compromised. And as a practical
matter, the product of FB pin bias current and larger FB
network impedances will cause increasing output voltage
error. (Nominal cancellation for 10k of FB Thevenin im-
pedance is included internally.)
Thermal Considerations
Care should be taken to ensure that the worst-case input
voltage and load current conditions do not cause exces-
sive die temperatures. The SO16 package is rated at
50
°
C/W when the four corner package pins are connected
to a good ground plane. (These corner pins are internally
fused to the die paddle for improved thermal perfor-
mance.) Die junction temperature is then a function of
ambient temperature and internal dissipation as follows:
T
J
= T
A
+
θ
JA
P
INT
Total internally dissipated power is composed of three
parts, quiescent power, DC switch loss and AC switch
loss. The AC switch loss will often dominate the total
dissipation, and this is unfortunately difficult to estimate
accurately.
Two options are suggested to the potential user. The first
is to observe the graphical data presented in the Typical
Applications section. Internal LT1777 dissipation vs load
current is given for output voltages of 5V and 3.3V, with
input voltages of 12V, 24V and 36V, and with sense
inductors of 0
μ
H, 1
μ
H, and 2.2
μ
H (Figures 9 and 11).
While it is true that the user’s ultimate circuit may use
somewhat different passive components than the ex-
amples given, it turns out that internal IC dissipation is not
very sensitive to these changes.
In cases where the user’s potential circuit differs signifi-
cantly from the examples given, an empirical method is
suggested. Operate the proposed power supply over the
applicable input voltage and load current ranges. Measure
the input power and output power, and calculate the
difference as “lost power.” This measured lost power
minus estimated inductor and diode dissipation yields a
figure for internal LT1777 dissipation. Fortunately, as
LT1777 internal dissipation dominates total lost power,
inductor and diode power need not be estimated very
accurately. Inductor power may be estimated as I
2
R where
I is the load current and R is the DC resistance of the
inductor. (Loss in the sense inductor is usually so small
that only the main inductor must be considered.) Diode
power may be estimated as 1/2 V
F
I DC, where V
F
is the
diode forward voltage, I is the load current and DC is the
duty cycle percentage when the diode is conducting.
Frequency Compensation
Loop frequency compensation is performed by connect-
ing a capacitor, or in most cases a series R/C, from the
output of the error amplifier (V
C
pin) to ground. Proper
loop compensation may be obtained by empirical meth-
ods as described in detail in Application Note AN19.
Briefly, this involves applying a load transient and observ-
ing the dynamic response over the expected range of V
IN
and I
LOAD
values.
As a practical matter, a second small capacitor, directly
from the V
C
pin to ground is generally recommended to
attenuate capacitive coupling from the V
SW
and V
D
pins. A
typical value for this capacitor is 100pF. (See Switch Node
Considerations).
Switch Node Considerations
In spite of the fact that the LT1777 is a low noise converter,
it is still possible for the part to cause problems by
“coupling to itself.” Specifically, this can occur if the V
SW
pin is allowed to capacitively couple in an uncontrolled
manner to the part’s high impedance nodes, i.e., SHDN,
SYNC, V
C
and FB. This can cause erratic operation such as
odd/even cycle behavior, pulse width “nervousness”, im-
proper output voltage and/or premature current limit
action.
APPLICATIO
S I
N
FOR
ATIO
U
W
U
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1777CS#PBF | 功能描述:IC REG BUCK ADJ 0.7A 16SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LT1777CS#TR | 功能描述:IC REG BUCK ADJ 0.7A 16SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LT1777CS#TRPBF | 功能描述:IC REG BUCK ADJ 0.7A 16SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LT1777CSPBF | 制造商:Linear Technology 功能描述:Sw. Regulator Step-Down Low Noise SOIC16 |
| LT1777I | 制造商:LINER 制造商全称:Linear Technology 功能描述:Low Noise Step-Down Switching Regulator |
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